Contamination of vacuum systems, their inner surfaces as well as the associated contamination of residual atmosphere inside the vacuum systems represents a major problem in analytical techniques and techniques employing beams of charged ions, electromagnetic radiation, etc. Also, contamination of vacuum systems by organic compounds causes complications during the process of layers or structures formation in the vacuum.
Numerous techniques are currently used in decontamination of vacuum systems for removing organic compounds. During the installation of vacuum systems, it is primarily mechanical and chemical methods for cleaning vacuum units and systems that are used. Known are also plasma cleaning methods of vacuum systems used during the production process. In vacuum systems which are in use, where contamination increases depending on the duration of operation not only on the walls of the system, but residual atmosphere contamination (of the gases) associated with it also increases, using the above-mentioned methods requires either complete or partial dismantling of the vacuum system.
Nowadays, in vacuum systems that are already in operation, decontamination of the surface is carried out at higher temperatures of the vacuum system. This, however, bears the risk of damaging some parts of the vacuum system by the higher temperatures. Moreover, this method is energetically demanding and time-consuming and although it creates more stable layer on the surface of the system, but considerable amount of the contaminants remains in the system in the form of residual compounds.
Another method used for reducing contamination of vacuum systems is a plasma decontamination device, which makes use of the fact that the oxygen radicals or hydroxyl radicals generated in the chamber of the decontamination device react with the contaminants inside the vacuum system, which results in the decomposition of the contaminants and their subsequent pumping out of the vacuum system into the pumping system. Nevertheless, this method of decontamination is time-consuming and the price of the plasma decontamination device is high. Another drawback of this method of decontamination is the interaction of the reactive particles with parts of the vacuum system, whereby this interaction is undesirable and may cause improper functioning of parts of the vacuum system or their corrosion.
Direct plasma decontamination in vacuum systems that are already in operation, in which the plasma reactor includes a vacuum chamber, has limited applicability due to the risk of the material, such as metals, being sprayed over the entire inner area of the vacuum system, which is associated with subsequent technological problems during using the vacuum systems, for example problems with formation of conducting layers on isolators or waveguides, etc.
Another well-known method for reducing the concentration of contaminants which are found in a vacuum system is the so-called Cryo can/Coldfinger/Cold trap decontamination device, which uses the undercooling of the surface area of the vacuum system to the temperature of liquid nitrogen followed by adsorption of hydro-carbon compounds onto this undercooled area, by which means the contaminants are efficiently removed from the residual atmosphere inside the vacuum chamber. The disadvantage of this method is especially the fact that the contaminants remain inside the system in which after finishing the cooling process they are released again from the undercooled areas back to the atmosphere of the vacuum system.
Photocatalytic materials are used in many fields of modern technology and nowadays these materials can be found in a number of common applications, such as decontamination of water, air, etc. The most frequently used material is nano-crystalline titanium dioxide TiO2, which is activated by UVA radiation. Other materials, such as ZnO or metal-doped TiO2, exhibiting photoactivity even under visible light irradiation, are also common in numerous applications. Most applications of photocatalytic processes take place under atmospheric pressure. Decontamination of the system using a photocatalyst is described, for example, in U.S. Pat. No. 5,462,674 (B. E. Butters, A. L. Powel), which deals with a method and system for photocatalytic cleaning of contaminated liquid, as well as in US patent application No 2003/0066975 (Masashi Okada), disclosing a system and method for reducing contamination in a microlithography system based on photocatalysis. The disadvantage of the method for the decontamination of gases or vacuum systems according to these patent documents, i.e. using only a photocatalytic layer, is a relatively low speed of decontamination, since the decontamination process takes place only in the particles adsorbed onto the surface of the photocatalytic layer and, especially in the vacuum, the spontaneous adsorption of the particles onto the surface at room temperature is rather slow.
The above-mentioned drawbacks have been overcome by the present invention, in which a surface covered with a photocatalytic layer, undercooled to an extremely low temperature, is used for decontamination. The adsorption of the particles of the inner atmosphere of the vacuum system onto the part of the inner surface of the vacuum system, whose temperature is lower than that of the environment, is considerably faster. As a lot more particles adheres to the surface of the photocatalytic layer during a short time due to undercooling, more particles are subsequently decomposed by the photocatalytic process. Another substantial benefit of the present invention is the fact that the efficiency of the photocatalytic process itself increases with a decreasing temperature. The goal of the invention is to eliminate or at least reduce the disadvantages of the background art, particularly enhance the efficiency of the decontamination of vacuum systems, improving at the same time the operating conditions of decontamination and making the decontamination process more affordable, not only from the point of view of purchase costs, but also operating and maintenance costs. Last but not least, the aim is to reduce the demands placed on the operator of the decontamination system.